(1) Field of the Invention
The present invention relates to hearing aids worn by users for auditory compensation.
(2) Description of the Related Art
Hearing aids of recent years are equipped with multiple functions such as directional control, noise suppression, and automatic volume adjustment. For example, hearing aids themselves determine the environment surrounding the user, such as the surrounding noise level, and control signal processing (hereinafter referred to as hearing-aid processing) according to the determined environment. By automatically controlling the hearing-aid processing according the surrounding environment in such a manner, the hearing aids are capable of providing the users with improved “hearing” (for example, see Patent Reference 1: Japanese Patent No. 3865600).
However, the sounds which the users wish to hear do not solely depend on the surrounding environment. The sounds which the users wish to hear change depending on the situation that the individual users are in and on the psychological status of the users. Therefore, with the above method in which the hearing aids automatically determine the surrounding environment and control the hearing-aid processing according to the determined environment, optimal “hearing” may not be provided to every user. Therefore, when there is a difference between the output sound of the hearing aid and the sound which the user wishes to hear, the user's intention needs to be conveyed to the hearing aid in some form.
In view of the above, conventional hearing aids generally have a switch or the like on the body or on a remote control that comes with a hearing aid for conveying the user's intention to the hearing aid. FIG. 8 is a block diagram illustrating the functional structure of a conventional hearing aid 100. A hearing-aid signal processing unit 115 generates an output signal from an input signal generated by an air-conduction microphone 111. Then, a receiver 116 outputs as a sound the output signal generated by the hearing-aid signal processing unit 115. The hearing-aid processing control unit 114 determines the surrounding environment based on an input signal, and outputs control information for controlling signal processing performed by the hearing-aid signal processing unit 115, according to the determined environment. Further, the user can input a control signal to the hearing-aid processing control unit 114 by using a switch or the like provided on a hearing-aid remote control 200 or on the body of the hearing aid 100.
Aside from this, as a method in which the user himself or herself adjusts the hearing aid, there is an example where the user is assisted in adjusting the hearing aid by storing in advance test acoustic data in a remote apparatus of the hearing aid, and providing the hearing aid with a mechanism that allows reproduction of the stored test acoustic data (for example, see Patent Reference 2: Japanese Unexamined Patent Application Publication No. 2007-028609).
In addition, in the fields other than hearing aids, a speech interface has been proposed as one of the hands-free input interfaces. The speech interface provides the users with easy usage without the need to use hands, and is thus applied to a variety of appliances such as computers, car navigations, and mobile phones. Hearing aids having a speech interface are not in practical use yet. However, since hearing aids are small appliances difficult for the users to handle, the speech interface is considered to be an effective replacement for manual input interface using a switch and the like.
Furthermore, in general, microphones include air-conduction microphones that detect sounds by detecting the air oscillations, and contact microphones that detect sounds by detecting the oscillations of the user's body parts such as bones or skin. Contact microphones include bone-conduction microphones that detect the oscillations of the user's bones, and skin-conduction microphones that detect the oscillations of the user's skin. Contact microphones generally have a structure in which an oscillation plate that detects sound oscillations is covered by an external sound insulation wall (case) (for example, see Patent Reference 3: Japanese Patent No. 3760173, Patent Reference 4: Japanese Unexamined Patent Application Publication No. 2007-101305, and Patent Reference 5: Japanese Unexamined Patent Application Publication No. 2007-259008). Further, contact microphone are characterized in being impervious to a noise getting mixed and capable of detecting small utterance compared to normal air-conduction microphones.